Method for the preparation of multiphase heterogeneous photoconductive compositions containing at least one pyrylium dye and an electrically insulating polymer

ABSTRACT

Multiphase heterogeneous compositions useful in electrophotography are formed from a combination in solution of at least one organic dye and an electrically insulating polymer. The dye is first dissolved in a solvent prior to addition of the polymer. The polymer is then stirred into the dye solution and the combined solution is coated on a support to form an electrophotographic layer. These heterogeneous compositions are useful as photoconductors or electrophotosensitizers and are characterized by a radiation absorption maximum that is substantially shifted from the absorption maximum of the dye and polymer when dissolved together to form a homogeneous composition.

Mates tot [72] Inventors Eugene 11 Grnrnan;

.lnmes Ml. flwens, both of Rochester, NY.

[21] Appl. No. 010,031

[22] Filed Apr. 10, 11960 [45] Patented Oct. 20, 11971 {73] Assignee Enntnmnn 11106111111 Cornnnny Rochester, N.l/.

[54] METIHIQD TOT t THE PlltElPAlltATllON 0E Mil/L'lllllllll/TSE HETIEROGENEOUS PHOTUEONDUETWE COMPOSllTlQNS QONTAIINHNG AT LEAST ONE MIRYILHIUM DYE AND AN lElLE CTlMCALLY llNSlUlLATllNG POLYMER 1M1 Claims, No Drawings 96/1.7, 260/3451, 260/345.9, 260/327 TH, 252/501 [51] lint. Cl (503g 5/00, 003g 7/00 [50] ll ielrl 011 Search 96/1.6, 1.7; 260/3451, 345.9, 327 TH; 252/501 [56] lllellerences Cited UNITED STATES PATENTS 3,052,540 9/1962 Greig... V 96 1 7 3,125,447 3/1964 Stewart 96/1.7

3,250,615 5/1966 Van Allan et al. 96/1 .7

3,488,705 1/1970 FOX et a1. 96/1.6

3,503,740 3/1970 De Selms 96/1.6 x FOREIGN PATENTS 1,091,715 11/1967 Great Britain 96/l.6

Primary Examiner-Charles E. Van Horn Assistant Examiner-John R. Miller Attorneys- W. H]. 1(line,.l. R, Frederick and T. Hiatt compositions are useful as photoconductors or electrophotosensitizers and are characterized by a radiation absorption maximum that is substantially shifted from the absorption maximum of the dye and polymer when dissolved together to form a homogeneous composition.

MlE'llll LlD Willi THE PlitlElAlilA'llllUN 01F MlUlLTlllPhiiAfilE lilllE'lllEliiUGlEhlEQU-d lPllllUTQEtlihlDllCTlWlE UU MlF USETiIQNS (IUNTAHNHNG AT LEAST UNE lPYlitlr'lhiiiJh i EililE AM!) 1 th! ELECTlFilCALLlr' llNSlJLATllNG lPUiLlIMlElt This invention relates to electrophotography and to photoconductive elements and structures useful in electrophotography. in addition, this invention relates to methods for preparing electrophotographic elements.

Electrophotographic imaging processes and techniques have been extensively described in both the patent and other literature, for example, Us. Pat. Nos. 2,221,776; 2,277,013; 2,297,691; 2,357,809; 2,551,582; 2,825,8l4; 2,833,648; 3,220,324; 3,220,831; 3,220,833 and many others. Generally, these processes have in common the steps of employing a nor mally insulating photoconductive element which is prepared to respond to imagewise exposure with electromagnetic radiation by forming a latent electrostatic charge image. A variety of subsequent operations, now well known in the art, can then be employed to produce a permanent record ofthe image.

One type of photoconcluctive insulating structure or element particularly useful in electrophotography utilizes a composition containing a photoconductive insulating material disposed in a resinous material. A unitary electrophotographic element is generally produced in a multilayer type of structure by coating a layer of the photoconcluctive composition onto a film support previously overcoated with a layer of conducting material or the photoconductive composition may be coated directly onto a conducting support of metal or other suitable conducting material. Such photoconductive compositions have shown improved speed and/or spectral response as well as other desired electrophotographic characteristics when one or more photosensitizing materials or addenda are incorporated into the photoconductive composition. Typical addenda of this latter type are disclosed in US. Pat. Nos. 3,250,615, 3,141,770 and 2,987,395. Generally photosensitizing addenda to photoconductive compositions are incorporated to effect a change in the sensitivity or speed of a particular photoconductor system and/or a change in its spectral response characteristics. Such addenda can enhance the sensitivity of an element to radiation at a particular wavelength or to a broad range of wavelengths where desired. The mechanism of such sensitization is presently not fully understood. The phenomenon, however, is extremely useful. The importance of such effects is evidenced by the extensive search currently conducted by workers in the art for compositions and compounds which are capable of photosensitizing photoconductive compositions in the manner described.

Usually the desirability of a change in electrophotographic properties is dictated by the end use contemplated for the photoconductive element. For example, in document copying applications the spectral electrophotographic response of the photoconductor should be capable of reproducing the wide range of colors which are normally encountered in such use. If the response of the photoconductor falls short of these design criteria, it is highly desirable if the spectral response of the composition can be altered by the addition of photosensitizing addenda to the composition. Likewise, various applications specifically require other characteristics such as the ability of the element to accept a high surface potential, and exhibit a low dark decay of electrical charge. it is also desirable for the photoconductive element to exhibit high speed as measured in a electrical speed or characteristic curve, a low residual potential after exposure and resistance to fatigue. Sensitization of many photoconductive compositions by the addition of certain dyes selected from the large number of dyes presently known has hitherto been widely used to provide for the desired flexibility in the design of photoconductive elements in particular photoconductor-containing systems. Conventional dye addenda to compositions have generally shown only a limited capability for overall improvement in the totality of electrophotographic properties which cooperate to produce a useful electrophotographic element or structure. The art is still searching for improvements in shoulder and toe speeds, improved solid area reproduction characteristics rapid recovery and useful electrophotographic speed from either positive or negative electrostatic charging.

A high speed heterogeneous or aggregate" photoconductive system was developed by William A. Light which overcomes many of the problems of the prior art. This aggregate composition is the subject matter of copending application, Ser. No. 674,005, filed Oct. 9, 1967, now abandoned and entitled Novel Photoconductive Compositions and Elements. The addenda disclosed therein are responsible for the exhibition of desirable electrophotographic properties in photoconductive elements prepared therewith. However, in accordance with the procedures described therein, the preparation of electrophotographic elements uses a solvent treatment step subsequent to the coating step. in an effort to avoid this secondary treatment step, a novel method of preparation of photoconductive compositions of the type described by Light is disclosed in copending Eugene P. Gramza application, Ser. No. 674,006, filed Oct. 9, 1967, now abandoned and entitled Method For The preparation Of lPhotoconductive Compositions. This latter method involves the high speed shearing of the photoconductive composition prior to coating and thus eliminates subsequent solvent treatment. However, it is often desirable to have photoconductive compositions of even higher speeds than those obtainable with the above compositions. Thus, copending Edward J. Seus application Ser. No. 764,302 filed Oct. 1, 1968, and entitled High Speed lElectrophotographic Elements And Method For Preparation Thereof discloses a technique for substantially increasing the speed of the above compositions. This technique involves forming electrophotographic layers by the above techniques and then overcoating such layers with a solution of suitable dye. This latter procedure uses a secondary coating step. Accordingly, there is a need for a method of obtaining high-speed photoconductive compositions which can be prepared in one coating step.

An additional problem encountered in forming such heterogeneous photoconductive compositions is that may of the dyes useful in preparing such compositions have several crystalline structures. Depending upon which crystalline structure of the dye is present when using the above techniques, the formation of the aggregate compositions can be relatively easy or quite difficult. Accordingly, there is a need for a method of obtaining high-speed photoconductive compositions in a manner which is independent of the crystalline structure of the dye.

It is, therefore, an object of this invention to provide the art of electrophotography with a novel method for preparing high-speed photoconductive compositions.

It is an additional object to provide a novel method for forming high-speed heterogeneous photoconductive compositions containing dye and polymer which method is independent of the crystalline structure ofthe dye.

It is another object to provide a novel process for forming high-speed electrophotographic elements.

These and other objects and advantages of the invention will become apparent from the following description of the invention.

it has been discovered that when the heterogeneous or aggregate photoconductive compositions of William A. Light are prepared by adding the ingredients in a certain prescribed manner formation of the heterogeneous composition is obtained with an unexpected increase in electrophotographic speed but without the necessity of any secondary treatment or coating steps. Furthermore, when the present method is used, the formation of such photoconductive compositions is found to be independent of the crystalline structure of the dye or dyes used. In particular, when the sensitizing dye is substantially completely dissolved in an organic coating solvent prior to addition of polymeric binder and photoconductor the electrophotographic speed can be substantially increased without the need for any aftertreatment. The aggregate compositions formed by the present method can be used as photoconductors or as sensitizers for other photoconductors.

The method of this invention is used to form heterogeneous multiple photoconductive compositions comprised of an organic sensitizing dye and an electrically insulating, film-forming polymeric material. The present method is relatively uncomplicated and provides results which are readily reproducible and which are relatively independent of the crystalline structure of the particular dye or dyes used. One of the essential features of the instant invention is the substantially complete dissolution of the sensitizing dye in a suitable solvent prior to the addition of any other addenda. After first dissolving the dye, the polymeric material is subsequently added with suitable stirring to dissolve the polymer. The combined solution is then coated on a suitable support which results in the formation of a separately identifiable multiphase composition, the heterogeneous nature of which is generally apparent when viewed under at least 2500X magnification, although such compositions may appear to be substantially optically clear to the naked eye in the absence of magnification. There can, of course, be a macroscopic heterogeneity Suitably, the dye-containing aggregate in the discontinuous phase is predominantly in the size range of from about 0.01 to 25 microns. However, it should be noted that when the heterogeneous compositions of the invention are used to sensitize a particulate photoconductor, sucl as zinc oxide, another discontinuous phase will be present which may not fall within this size range.

in general, the heterogeneous compositions formed by the present method are multiphase organic solids containing dye and polymer. The polymer forms an amorphous matrix or continuous phase which contains a discrete discontinuous phase as distinguished from a solution. The discontinuous phase contains a significant portion of the dye present and generally a predominant portion of the dye present is in this discontinuous phase. The dye in the discontinuous phase can be considered as being in particulate form; however, that phase need not be comprised wholly of dye. It is believed that in some instances the discontinuous phase may be comprised of a cocrystalline complex of dye and polymer; however, it is also believed that all of the aggregates which can be formed in accordance with the method of this invention are not necessarily comprised of dye and polymer. Preferably, substantially all of the dye present in this system in is the discontinuous phase. When the present compositions are used in conjunction with an organic photoconductor, the resultant photoconductive composition generally contains only two phases as the photoconductor usually forms a solid solution with the continuous polymer phase. On the other hand, when the present multiphase compositions are use in conjunction with a particulate photoconductor, three phases may be present. In such a case there would be a continuous polymer phase, a discontinuous phase containing dye as discussed above and another discontinuous phase comprised of the particulate photoconductor. Of course, the present multiphase compositions may also contain additional discontinuous phases of trapped impurities, etc. Another feature characteristic of the heterogeneous compositions formed in accordance with this invention is that the wavelength of the radiation absorption maximum characteristic of such compositions is substantially shifted from the wavelength of the radiation absorption maximum ofa substantially homogeneous dye-polymer solid solution formed of similar constituents. The new absorption maximum characteristic of the aggregates formed by this method is not necessarily an overall maximum for this system as this will depend upon the relative amount of dye in the aggregate. Such an absorption maximum shift in the formation of multiphase heterogeneous systems for the present invention is generally of the magnitude of at least about mp. If mixtures of dyes are used, one dye may cause an absorption maximum shift to a long wavelength and another dye cause an absorption maximum to a shorter wavelength. In such cases, a formation of the heterogeneous compositions can more easily be identified by viewing under magnification.

Sensitizing dyes and electrically insulating polymeric materials are used in forming these heterogeneous compositions. Typically, pyrylium dyes, including pyrylium, thiapyrylium and selenapyrylium dye salts are useful in forming such compositions. Such dyes include those which can be represented by the following general formula:

Ra Bo wherein R", R", R, R", and R' can each represent (a) a hydrogen atom; (b) an alkyl group typically having from one to 15 carbon atoms, such as methyl, ethyl, propyl, isopropyl, butyl, tertiary butyl, amyl, isoamyl, hexyl, octyl, nonyl, dodecyl, etc., (c) alkoxy groups like methoxy, ethoxy, propoxy, butoxy, amyloxy, hexoxy, octoxy, and the like; and (diaryl groups including substituted aryl groups such as phenyl, 4- diphenyl, alkylphenyls as 4-ethylphenyl, 4-propylphenyl, and the like, alkoxyphenyls as 4-ethoxyphenyl, 4-methoxyphenyl, 4-amyloxyphenyl, 2-hexoxyphenyl, 2-methoxyphenyl, 3,4- dimethoxyphenyl, and the like, B-hydroxy alkoxyphenyls as 2- hydroxyethoxyphenyl, 3-hydroxyethoxyphenyl, and the like, 4-hydroxyphenyl, halophenyls as 2,4-dichlorophenyl, 3,4- dibromophenyl, 4-chlorophenyl, 3,4-dichlorophenyl, and the like, azidophenyl, nitrophenyl, aminophenyls as 4- diethylaminophenyl, 4-dimethylaminophenyl and the like, naphthyl; and vinyl substituted aryl groups such as styryl, methoxystyryl, diethoxystyryl, dimethylaminostyryl, l-butyl- 4-p-dimethylaminophenyll ,3-butadienyl, B-ethyl-4- dimethylaminostyryl, and the like; and where X is a sulfur, oxygen or selenium atom, and Zis an anionic function, including such anions as perchlorate, fluoroborate, iodide, chloride, bromide, sulfate, periodate, p-toluenesulfonate, and the like in addition, the pair R" and R as well as the pair R" and R can together be the necessary atoms to complete an aryl ring fused to the pyrylium nucleus. Typical members of such pyrylium dyes are listed in table I.

TABLE 1 Compound Number Name ofCompound l 4-[4 bis-(2-chloroethyl)aminophenyl]-2,6-

diphenylthiapyrylium perchlorate 2 4-(4-dimethylaminophenyl)-2,6-

diphenylthiapyrylium perchlorate 3 4-(4-dimethylarninophenyl)-Z,6-

diphenylthiapyrylium fluoroborate 4 4-(4-dimethylamino-Z-methylphenyl)-2,6- diphenylpyrylium perchlorate 5 4-(4-bis(Z-chlorocthyl)aminophenyll-Z-(4- methoxyphcnyl)-6-phenylthiapyrylium perchlorate 6 4-(4-dimethylaminophenyl)-Z,6-

diphenylthiapyrylium sulfate 7 4-(4-dimcthylumin0phenyl)-Z,6-

diphenylthiapyrylium p-toluenesulfonate 8 4-(4 -dimethylaminophenyl)-2,6-diphenylpyryliump-toluenesulfonate 9 2-(2,4-dimethoxyphenyl)-4-(4- dimethylaminop'henyl)benzo(b)pyrylium perchlorate 2,6-bis(4-ethylphenyl)-4-(4- dimethylaminophenyl)thiapyrylium perchlorate l l 4-(4-dimethylaminophenyl)-2-(4-methoxyphenyl)-6- phenylthiapyrylium perchlorate 4-(4-dimethylaminophenyl)-2-(4-ethoxyphenyl)-6- phenylthiapyrylium perchlorate 4-(4-dimethylaminophenyl)-2-(4-methoxyphenyl)-6- (4-methylphenyl)pyrylium perchlorate 4-(4-diphenylaminophenyl)-2.6-

diphenylthiapyrylium perchlorate 2,4,6-triphenylpyrylium perchlorate 4-(4-methoxyphenyl)-2,6-diphenylpyrylium perchlorate 4-(2,4-dichlorophenyl)-2,6-diphenylpyrylium perchlorate all 4-(lfi dichlorophenyl)-2,-diphenylpyrylium perchlorate 1.6-bis(4-methoxyphcnyl)-4phenylpyryliam perchlorate 6-(4-methoxyphenyl)-2.4-diphcnylpyrylium perchlorate 2-(3,4-dichlorophenyl)-4-t4-methoxyphenyl) 6- phenylpyrylium perchlorate 4-t4-amyloxyphcnyl)2.6-bis(4 ethylphenyllpyrylium perchlorate ll-(karnyloxyphenyl)-2,6-bis(4- methoxyphenyljpyrylium perchlorate 2,4,64riphenylpyrylium fluoroborate 2,6-bis(4'ethylphenyl)-4-t4- methoxyphenynpyrylium perchlorate 2.6-bist4ethylphenyl)-4-(4- methoxyphenyl)pyrylium fluoroborate 6 (3.4 diethoxystyry])-2, $-diphenylpyryliunt perchlorate 6(3,4 diethoxyfi amylstyryl) ld-diphcnyl yrylium fluoroborate t-(4dimethylamino-fi-ethylstyrylylddi henylpyrylium fluoroborate 6-( l-n-amyl-d-p-dimethylaminophcnyl-l ,J

hutadicnyl)-2,4-diphenylpyrylium lluorohorate 6-(4-dimethylaminostyrylyZ,J-diphenyl yrylium fluoroborate o lu-ethylfifi bifldintethylaminophenyl)vinylene1- 2,4-diphenylpyrylium flaoroborate l-butyl4-p-dimethylaminophenyl-l,3

butadienyll-2,4-diphenylpyrylium fluoroborate 6%4-dimethylaminostyryl)-lt4diphenylpyrylium perchlorate 6'[B fl-htst4-dintethylaminophenyllvinylene]-2,4-

diphcnylpyrylium perchlorate ljvhist-1-dimethylaminostyryl)Lphcnylpyrylium perchlorate o-toLmethyl-4-dtmcthylaminostyryl)-2,4-

diphenylpyrylium l'luoroborate 6-l l-ethyl-4 l4-1.limclhylamirtopheny|)-l.3

hutadicnyll-2,4-diphenylpyrylium fluoroborate tS-{Bfi-bifl4-dimcthylaminophenyllvinyleneLZA- diphenylpyrylium fluoroborate b l l-methyl-l'l 4-dimelhylaminophcnyll-l.3-

hatadicnyl1-3.4-diphenylpyrylium fluoroborate 4i t4-t.ltrnethylarninophenyl)-Z,6-tlipheny|pyryliun\ perchlorate 2,6-bis(4-ethylphenyll-4-phenylpyrylium perchlorate 1.6 hist4-ethylphenyl)4methoxyphcnylthiapyrylium fluorohoratc 1.4.64riphenylthiapyrylium perchlorate l-(4-rnethoxyphenyl)-2,o-diphenylthiapyrylium perchlorate o-( l-nterhoxyphenyll:,4-diphenyllhiapyryliunt perchlorate 2,6bistJ'methoxyphenyl)A-phenylthiapyrylium perchlorate 442,4dichlorophenyl)-2,b-diphenylthinpyrylium perchlorate 2,-l,t -tri(4-methoxyphcnyl)thiupyrylium perchlorate 2,6-bist4-ethylphcnyll4-phcnylthiapyrylium perchlorate -l-t4-amyloxyphenyl)-2,6-bis(4- ethylphenylHhiapyrylitmt perchlorate \1-(4-dimethylaminostyryl)-2,J-tliphenylthiupyrylium perchlorate 2AJJ-triphenylthiapyrylium fluoruhoratc l,lfit-triphenylthinpyrylium sulfate -ll-(-l-melhoxyphenyll-Z,h-tliphenyllhiapyrylium I'luorohuratc lwlfiariphenylthiapyrylium chlorlde Z-(J-amyloxyphenyl1-4,o-dlphenyllhiapyrylium tltmrohorate 444-amyloxyphcnyl)'l,o-bis(4- niethoxyphcnyl)thtapyrylium perchlorate Z,6-bis(4-ethylphcnyl1-4-(4- ntclhoxyphenyl)thtapyrylium perchlorate Jamisyl-2,b his(4 naimyloxphenyl)thiapyrylium chloride l-l/Lfl-bifl4-dimethylamniophenyl)vinylenel-dla diphenylthiapyryliunt perchlorate 6-(h2-ethyl -l-dintcthylanunostyryl)ZA- diplteltylthiapyryltunt perchlorate 1-(3,4-dicthoxystvryl)-4,h-diphcnylthiapyrylium perchlorate 3,4,6 triunisylthlapyryliunr perchlorate tS-ethyl-2,4-diphenylpyrylium fluorohoratc 2,6 hist4-ethylphenyl1-444- methoxyphenyl)thiapyryliunt chloride tS-lfi,fl-his(d-dimclhylaminophenyl)vinylene]-2,4-

di(4-ethylphcnyl)pyryliunt perchlorate ljrhistJ-antyloxyphenyl|-4-(4 mcthoxyphcnyltthntpyrylium perchlorate IS-(3,4-diethoxy-[Lethylstyryl)-2,4-diphcnylpyrylium fluorohorate 71 2 (4-ethylphenyl )--l.6-diphenylthiapyrylium perchlorate 72 1,6-diphenyl-4-t4-methoxyphenyl lthiapyrylium perchlorate Particularly useful dyes in forming the feature aggregates are pyrylium dye salts having the formula:

wherein:

R and R can each be phenyl radicals, including substituted phenyl radicals having at least one substituent chosen from alltyl radicals of from one to six carbon atoms and alkoxy radicals having from one to six carbon atoms;

R; can be an alkylamino-substitutedl phenyl radical having from one to six carbon atoms in the alkyl moiety, and including dialkylarninc-substituted and haloalkylamino substituted phenyl radicals;

X can be an oxygen or a sulfur atom; and

Zis the same as above While the pyrylium dyes are preferred in preparing the present heterogeneous or aggregate systems, other photographic spectral sensitizing dyes that activate light exposed areas of photographic compositions can be utilized in the insulating polymer ofsuch a system.

Electrically insulating, film-forming polymers suitable for the formation of electrophotographic compositions containing the aggregate photoconductivc compositions made by this invention include polycarbonates and polythiocarbonates. polyvinyl ethers, polyesters, poly-a-olefins, phenolic resins, and the like. Mixtures of such polymers can also be used. Such polymers include those which function in the formation of the aggregates as well as functioning as binders which hold the photoconductive compositions to a suitable support. Typical polymeric materials from these classes are set out in table 2.

TABLE 2 Number Polymeric Material l polystyrene olyvinyltoluene polyvinylanisole polychlorostyrene polyu-mcthylstyrene polyacenaphthalene poly(vinyl isobutyl ether) poly(vinyl cinnamatc) poly(vinyl benzoate) poly(vinyl naphthoate) polyvinyl carbazole poly(vinylene carbonate) polyvinyl pyridine poly(vinyl acetal) poly(vinyl butyral) poly(ethyl methacrylate) po|y(butyl methacrylate) poly(styrene-co-butadicne) poly(styrene-co-methyl methacrylate) poly(styrene-co-ethyl acrylate) poly(styrcne-co-acrylonitrile) poly(vinyl chloridc-co-vinyl acetate) poly(vinylidene chloride-co-vinyl acetate) poly(4,4'-isopropylidcnediphenyl-co-4,4'-

isopropylidenediphenyl-co-4.4'- isopropylidencdicyclohexyl carbonate) poly[4,4'-isopropylidenebis( 2.6- dibromophenyhcarbonatcl poly]4.4'-isopropylidenebis(2,6

dichlorophenyl)carbonate] poly]4,4-isopropylidcncbis(2,6- dimcthylphenyl)carbonate] poly(4,4'-isopropylidenediphenyl-co-l .4-

cyclohexyldimethylcarbonate) poly(4.4'-isopropylidenediphenyl tcrephthalate-coisophthalatc) poly(3,3'-ethylenedioxyphenyl thiocarbonate) poly(4 4'-isopropylidenediphenyl carbonate-coterephihalate) poly(4.4-isopropylidcriediphenyl carbonate) poly(4,4'-isopro ylidenediphenyl thiocarbonatc) poly(2,2-butanebis-4-phenyl carbonate) poly(4,4'-isopropylidenediphenyl carbonate-blockethylene oxide) oly(4,4 isopropylidenediphenyl carbonate-blocktetramethyleneoxidc) poly]4.4'-isopropylidenebis(2- mcthylphenyhcarbonate] poly(4,4-isopropylidenediphenyl-co-l,4-phenylene carbonate) poly(4,4'-isopropylidenediphenyl-co-l,S-phenylene carbonate) poly(4,4-isopropylidencdiphenyl-co-4.4diphenyl carbonate) polyt4.4'-isopropylidenediphenyl-co-4,4-

oxydiphenyl carbonate) polyt4,4'-isopropylidenediphenyl-co-4.4'-

carbonyldiphenyl carbonate) poly(4,4'-isopropylidcnediphenyl-co-4,4'-

ethylenediphcnyl carbonate) poly] 4,4'-methylenebis(2-methylphenyl)carbonate] poly]l,l-(p-bromopl1cnylethune)bis(4- phenyl)carbonate] poly]4,4-isopropylidenediphenyl-co-sulfonylbis(4- phenyl)carbonate] poly] l .l-cyclohexanebis(4-phenyl)carbonate] poly(4,4'-isopropylidenediphenoxydimethylsilane) poly[4,4'-isopropylidene bis(2-chlorophenyl)- carbonate] polylmono'.a'-ta:tramethyl-p-xylylenebis(4-phenyl carbonatel] polythexal'luoroisopropylidcnedit-phenyl carbonate) poly]dichlorotetralluoroisopropylidenedi-4-phenyl carbonate) poly(4.4'-isopropylidenediphenyl-4.4-

isopropylidene dibenzoate) poly(4.4-isopropylidenedibcnzyl-4,4-isopropylidene.

dibenzoate) oly(4 4'-isopropylidcncdi-lnaphthyl carbonate) poly]4.4'-isopropylidenebis(phenoxy-4-phenyl sulfonate)] aectophenone-formaldehyde resin poly]4.4-isoprupylidcncbis(phenoxyethyl)-coethylene tcrephthalate] phenol-formaldehyde resin polyvinyl acetophenone chlorinated polypropylene chlorinated polyethylene polyt2.6-dimethylphenylene oxide) poly(neopcntyl-Z.6 naphthalenedicarboxylate) poly(ethylene terephthalate-co-isophthalatc) polyt1,4-phenylene-co-l.B-phenylenc succinatc) poly(4,4-isopropylidenediphenyl phenylphusphonatc) poly(m-phenylcurboxylate) poly( l 4-cyclohexanedimcthyl terephthalate-coisophthalate) 70 poly(tetramcthylenc succinatc) 7l poly(phenolphthalcin carbonate) 72 poly(4-chloro-l .3-phenylene carbonat 73 poly(2-methyl-l ,3-phenylene carbonate) 74 poly( l,l-bi-2-naphthyl thiocarbonale) 75 poly(diphenylmethane bis-4-phenyl carbonate) 76 poly[2.2-(S-mcthylbutane)bis-4-phenyl carbonate] 77 poly]2,2-(3,3-dimethylbutane)bis-4-phenyl carbonate] 78 poly{l,l-[ l-( l-naphlhylHbis-d-phenyl carbonate 79 poly]2,2-(4-methylpentane)bis-4-phenyl carbonate] 8O poly[4,4'-(2-norb0rnylidene)diphenyl carbonate] 8] poly[4,4-(hexahydro-4.7-methanoindunfiylidenchliphenyl carbonate] 82 poly(4.4-isopropylidenediphenyl carbonate-blockoxytetramcthylene) Especially useful polymers for forming the heterogeneous compositions in accordance with the present method are compounds numbered 28, 30-47, 49, 51, 53, 54 and 76-82 as listed in table 2 above.

the following recurring unit:

wherein:

R and R when taken separately, can each be a hydrogen atom, an alkyl radical such as methyl, ethyl, butyl, tertiary butyl, pentyl, hexyl, heptyl, octyl, nonyl, decyl and the like including substituted alkyl radicals such as trifluoromethyl, etc., and an aryl radical such as phenyl and naphthyl including substituted aryl radicals having such substituents as a halogen, alkyl radicals offrom one to five carbon atoms, etc.; and R and R when taken together, can represent the carbon atoms necessary to form a cyclic hydrocarbon radical including cycloalkanes such as cyclohexyl and polycycloalkanes such as norbornyl, the total number of carbon atoms in R and R being up to 19;

propyl, isopropyl,

R and R, can each be hydrogen, an alkyl radical of from one to five carbon atoms or a halogen such as chloro, bromo,

iodo, etc.; and

R is a divalent radical selected from the following:

0 S 0 ll ll I Among the hydrophobic carbonate polymers particularly wherein:

each R is a phenylene radical including halo substituted phenylene radicals and alkyl substituted phenylene radicals; and R and R are as described above. Such compositions are disclosed, for example in U.S. Pat. Nos. 3,028,365 and 3,317,466. Preferably polycarbonates containing an alkylidene diarylene moiety in the recurring unit such as those prepared with Bisphenol A and including polymeric products of ester exchange between diphenvlcarbonate anrl 27-hi.e 4.

hydroxyphenyl propane are useful in the practice of this invention. Such compositions are disclosed in the following U.S. Pat. Nos. 2,999,750; 3,038,874; 3,038,879; 3,038,880; 3,106,544", 3,106,545; 3,106,546; and published Australian Pat. specification No. 19575/56. A wide range of film-forming polycarbonate resins are useful, with completely satisfactory results being obtained when using commercial polymeric materials which are characterized by an inherent viscosity of about 0.5 to 0.6. In addition, a high molecular weight material such as a high molecular weight Bisphenol A polycarbonate can be very useful. Preferably, such high molecular weight materials have an inherent viscosity of greater than about 1 as measured in l,2-dichloroethane at a concentration of 0.25 g./100 ml. and a temperature of about 25 C. The use of high molecular weight polycarbonate, for example, facilitates the formation of aggregate compositions having a higher dye concentration which results in increased speeds.

The present invention can readily be used for enhancing the sensitivity and extending the spectral range of sensitivity of a variety of organic photoconductors and inorganic photoconductors including both nand p-type photoconductors. A typical example of an inorganic photoconductor would be zinc oxide. The present invention can be used in connection with many organic, including organometallic, photoconducting materials which have little or substantially no persistence of photoconductivity. Representative organometallic compounds are the organic derivatives of Group Illa, lVa, and Va metals such as those having at least one amino-aryl group attached to the metal atom Exemplary organometallic compounds are the triphenyl-p-dialkylaminophenyl derivatives of silicon, germanium, tin and lead, the tri-p-dialkylaminophenyl derivatives of arsenic, antimony, phosphorus, bismuth boron, aluminum, gallium, thallium and indium. Useful photoconductors of this type are described in copending Goldman and Johnson U.S. Pat. application, Ser. No. 650,664, filed July 3, 1967 and Johnson application, Ser. No. 755,711, filed Aug. 27, 1968.

An especially useful class of organic photoconductors is referred to herein as organic amine" photoconductors. Such organic photoconductors have as a common structural feature at least one amino group. Useful organic photoconductors which can be spectrally sensitized in accordance with this invention include, therefore, arylamine compounds comprising (l) diarylamines such as diphenylamine, dinaphthylamine, N,N'-diphenyl-benzidine, N-phenyl-1-naphylamine, N-phenyI-Z-naphthylamine, N,N'-diphenyl-p-phenylenediamine, 2- carboxy-S-chloro-4-methoxydiphenylamine, p-anilinophenol, N,N'-di-2-naphthyl-p-phenylenediamine, those described in Fox U.S. Pat. No. 3,240,597, issued Mar. 15, 1966, and the like, and (2) triarylamines including (a) nonpolymeric triarylamines, such as triphenylamine, N,N,N'-N'-tetraphenylm-phenylenediarnine, 4-acetyltriphenylamine, 4-hexanoyltriphenylamine, 4-lauroyltriphenylamine, 4-hexyltriphenylamine, 4-dodecyltriphenylamine, 4,4'-bis(diphenylamino)benzil, 4,4'-bis(diphenylamino)benzophenone and the like, and (b) polymeric triarylamines such as poly [N,4"-(1-l,l l,N-triphenylbenzidine)], polyadipyltriphenylamine, polysebacyltriphenylamine, polydecamethylenetriphenylamine, poly-N-(4-vinylphenyl)diphenylamine, poly- N-(vinylphenyl)-a,a-dinaphthy1amine and the like. Other useful amine-type photoconductors are disclosed in U.S. Patent 3,180.730. issued April 27, 1965.

Useful photoconductive substances capable of being sensitized in accordance with this invention are disclosed in Fox U.S. Pat. No. 3,265,496, issued Aug. 9, 1966, andinclude those represented by the following general formula:

R[IIIT]Q wherein T represents a mononuclear or polynuclear divalent aromatic radical, either fused or linear (e.g., phenyl, naphthyl, biphenyl, binaphthyl, etc.), or a substituted divalent aromatic radical of these types wherein said substituent can comprise a member such as an acyl group having from one to about six carbon atoms (e.g., acetyl, propionyl, butyryl, etc.), an alkyl group having from one to about six carbon atoms (e.g., methyl, ethyl, propyl, butyl, etc.), an alkoxy group having from one to about six carbon atoms (e.g., methoxy, ethoxy, propoxy, pentoxy, etc.), or a nitro group; M represents a mononuclear or polynuclear monovalent aromatic radical, either fused or linear (e.g., phenyl, naphthyl, biphenyl, etc.), or a substituted monovalent aromatic radical wherein said substituent can comprise a member, such as an acyl group having from one to about 6 carbon atoms (e.g., acetyl, propionyl, butyryl, etc.), an alkyl group having from one to about six carbon atoms (e.g., methyl ethyl, propyl, butyl, etc.), an alkoxy group having one to about six carbon atoms (e.g., methoxy, propoxy, pentoxy, etc.), or a nitro group; O can represent a hydrogen atom, a halogen atom or an aromatic amino group, such as MNH-; b represents an integer from l to about 12; and, R represents a hydrogen atom, a mononuclear or polynuclear aromatic radical, either fused or linear (e.g., phenyl, naphthyl, biphenyl, etc.), a substituted aromatic radical wherein said substituent comprises an alkyl group, an alkoxy group, an acyl group, or a nitro group, or a po1y(4-vinylphenyl) group which is bonded to the nitrogen atom by a carbon atom of the phenyl group.

Polyarylalkane photoconductors are particularly useful in producing the present invention. Such photoconductors are described in U.S. Pat. No. 3,274,000, French Pat. No. 1,383,461 and in copending application of Seus and Goldman titled Photoconductive Elements Containing Organic Photoconductors, Ser. No. 627,857, filed Apr. 3, 1967 now Pat. No. 3,542,544. These photoconductors include leuco bases of diaryl or triaryl methane dye salts, 1,1,1-triarylalkanes wherein the alkane moiety has at least two carbon atoms and tetrarylmethanes, there being substituted an amine group on at least one of the aryl groups attached to the alkane and methane moieties of the latter two classes of photoconductors which are nonleuco base materials.

Preferred polyarylalkane photoconductors represented by the formula can be wherein each of D, E and G is an aryl group and J is a hydrogen atom, an alkyl group, or an aryl group, at least one of D, E and G containing an amino substituent. The aryl groups attached to the central carbon atom are preferably phenyl groups, although naphthyl groups can also be used. Such aryl groups can contain such substituents as alkyl and alkoxy typically having one to eight carbon atoms, hydroxy, halogen, etc., in the ortho, meta or para positions, ortho-substituted phenyl being preferred. The aryl groups can also be joined together or cyclized to form a fluorene moiety, for example. The amino substituent can be represented by the for mula wherein each L can be an alkyl group typically having one to eight carbon atoms, a hydrogen atom, an aryl group, or together necessary atoms to form a heterocyclic amino group typically having five to six atoms in the ring such as morpholino, pyridyl, pyrryl, etc. At least one of D, E, and G is preferably p-dialkylaminophenyl group. When J is an alkyl group, such an alkyl group more generally has one to seven carbon atoms.

Representative useful polyarylalkaine photoconductors include the compounds listed in table 3.

TABLE3 Schlesinger Compound Number Name ofCompound l 4,4-benzylidene bistN,N-diethyl-m-toluidinc) 2 4',4"-dinmino-4-dirnethylamino-2,2"- dimethyltriphenylmethane 3 4',4"-bis(diethylamino)-2,6-dichloro-2,2"-

dimethyltriphenylmethane 4 4,4"-bis(diethylamino)-2,2"-

dimethyldiphenylnaphthylmcthane 5 2',2"-dimethyl-4,4',4"-

trls(dimethylaminoltriphenylmethane 6 4,4"-bis(diethylamino)-4-dimethylamino-2',2"-

dimethyltriphenylmethanc 7 4',4"-bis(diethylamino)-2-chloro-2,2"-dirnethyl-4- dimethylaminotriphenylmethane 8 4',4"-bis(diethylamino )-4-dimethylamino-2,2',2"-

trimethyltriphenylmethane 9 4',4"-bis(din1ethylamino)-2'chloro-2',2"

dimethyltriphenylmethanc 4',4"-bis(dimethylamino)-2,2"-dimethyl-4- mcthoxytriphenylmethnne bis(4-diethylamino)-l ,1 ,1 -triphenylcthane bis(4-diethylamino)tetraphenylmelhane 4',4"-bis(benzylethylamin0)-2,2"-

dimethyltriphenylmethane 4,4"-bis(diethylumino)-2.2"- diethoxytriphenylmethane 4,4'-bis(dimethylamino)- l ,1, 1 -triphenylethanc l-(4-N,N-dimethylaminophenyl l l -diphcnylethane 4-dimethylnrninotetruphcnylmclhanc 4-diethylaminotetraphcnylmethane Another class of photoconductors useful in this invention are the 4-diarylamino-substituted chalcones. Typical compounds of this type are low molecular weight nonpolymeric ketones having the general formula:

wherein R, and R are each phenyl radicals including substituted phenyl radicals and particularly when R is a phenyl radical having the formula:

where R;, and R are each aryl radicals, aliphatic residues of one to 12 carbon atoms such as alkyl radicals preferably having one to four carbon atoms or hydrogen. Particularly advantageous results are obtained when R, is a phenyl radical including substituted phenyl radicals and where R is diphenylaminophenyl, dimethylaminophenyl or phenyl.

Other photoconductors which can be used with the present aggregate compositions include rhodamine B, malachite green, crystal violet, phenosafranine, cadmium sulfide, cadmium selenide, parachloranil, benzil, trinitrofluorenone, tetranitrofluorenone, etc

The following table 4 comprises a partial listing of U.S. Patents disclosing a wide variety or organic photoconductive compounds and compositions which can be improved with respect to speed, sensitivity, and/or regeneration when incorporated into the feature compositions and elements of this invention.

The following table 4 comprises a partial listing of U.S. Patents disclosing a wide variety of organic photoconductive compounds and compositions which are also useful.

TABLE 4 'lnventor U.S. Pat. No.

Hocgl ct 111. 3,037,861 Sues et :11. 3,041,165 3,066,023

In preparing photoconductive compositions in accordance with this invention, useful results are obtained when an organic, including organometallic, photoconductor is present in an amount equal to at least about k percent by weight oftotal solids added to the coating solvent. The upper limit of the amount of photoconductor present can be varied widely with up to 99 percent by weight of total solids being useful. A preferred weight range of the photoconductor is from about 10 to about weight percent. Of course, ifit is desired to use the present aggregate compositions alone as the photoconductive substance, then no photoconductor would be added.

The organic coating solvents useful for preparing the present compositions can be selected from a variety of materials. Useful liquids are hydrocarbon coating solvents, including substituted hydrocarbon solvents, with preferred materials being halogenated hydrocarbon solvents. The requisite properties of the solvent are that it be capable of dissolving the sensitizing dye and capable of dissolving or at least highly swelling the polymeric ingredient of the present compositions. In addition, it is helpful if the solvent is volatile preferably having a boiling point of less than about 200 C. Particularly useful solvents include halogenated lower alkanes having from one to three carbon atoms, such as dichloromethane, dichloroethane, dichloropropane, trichloromethane, trichloroethane, tribromomethane, trichloromonofluoromethane, trichlorotrifluoroethane, etc.; halogenated benzene compounds such as chlorobenzene, bromobenzene, dichlorobenzene, etc.; and the like. Mixtures of solvents can also be used.

The concentration of dye which is first substantially completely dissolved in the coating solvent can be varied considerably, being limited, of course, by the solubility of a particular dye in a particular solvent and the the desired dye concentration in a particular composition. Higher dye concentrations generally give rise to resultant photoconductive compositions of higher or faster electrophotographic speeds. Useful results are obtained by using the described dyes in amounts of from about /2 to about 30 percent by weight of the total solids added to the coating composition.

The dye or dyes used in accordance with this invention are mixed into the coating solvent and stirred for a period of time at about room temperature (20 C.) to insure complete dissolution of the dye. Generally stirring for a period of up to about 2 to 3 hours is sufficient to obtain substantially complete dissolution of the dye. For convenience, the dye is usually dissolved at about room temperature; however, elevated temperatures can be used to speed dissolution. Of

course, care must be taken not to exceed the boiling point of the solvent. The time of stirring will vary depending upon the dye concentration and the total amount of solution being prepared. After the dye is in solution, the polymeric binder is then added and the solution is stirred for a period of time with stirring for 2 to 3 hours generally being sufficient. Next, the photoconductor is added, if desired, and the combined solution is stirred briefly. At this point the resultant dope is ready for coating without further treatment. The dope is then coated onto a suitable conducting support and allowed to dry. Drying can be accomplished by any convenient means such as simply allowing the solvent to evaporate at ambient conditions. The coating can also be dried by circulating air or gentle heating with care being taken to avoid any eat damage. The aggregate composition is thus formed upon coating and drying of the dope without the need for aftertreatment.

Coating thicknesses of the present photoconductive compositions on a support can vary widely. More generally, a coating in the range of about to about 1,250 before drying is useful for the practice of this invention. The preferred range of coating thickness is found to be in the range from about 50p to about 750p. before drying although useful results can be obtained outside of this range.

Suitable supporting materials for coating the photoconductive layers of the present invention can include any of a wide variety of electrically conducting supports, for example, paper (at a relative humidity above 20 percent), aluminum foilpaper laminates; metal foils such as aluminum foil, zinc foil, etc.; metal plates, such as aluminum, copper, zinc, brass and galvanized plates; vapor deposited metal layers such as silver, nickel, aluminum and the like coated on paper or conventional photographic film bases such as cellulose acetate, polystyrene, poly(ethylene terephthalate), etc. Such conducting materials as nickel can be coated by vacuum deposition on transparent film supports in sufficiently thin layers to allow electrophotographic elements prepared therewith to be exposed from either side of such elements. An especially useful conducting support can be prepared by coating a support material such as poly(ethylene terephthalate) with a conducting layer containing a semiconductor such as cuprous iodide dispersed in a resin. Such conducting layers both with and without insulating barrier layers are described in US. Pat. Nos. 3,245,833 and 3,428,451. Likewise, a suitable conducting coating can be prepared from the sodium salt of a carboxyester lactone of maleic anhydride and a vinyl acetate polymer. Such kinds of conducting layers and methods for their optimum preparation and use are disclosed in U.S. Pat. Nos. 3,007,901 and 3,267,807.

The present technique of substantially completely dissolving the sensitizing dye in a coating solvent prior to addition of either photoconductor or binder, gives rise to a totally unexpected advantage. This dye first" technique makes it possible to form aggregate photoconductive compositions having a higher dye concentration than has been heretofore possible in a single coating operation. The higher dye concentration in the aggregate composition results in higher electrophotographic speeds. ln fact, the speeds obtainable in this one coating, dye first technique are equivalent to the speeds obtained by the multiple dye overcoat technique described in the Seus application referred to above. Furthermore, the present technique can consistently produce high-speed photoconductive coatings without the necessity for a second coating operation. The present technique also allows better control of the quality as well as the speed of the finished compositions. Superior electrical performance is also obtained when coatings prepared by the present technique are subjected to regeneration tests wherein the electrophotographic element is repeatedly charged and exposed. Additionally, the present method makes it possible to readily produce high-speed photoconductive compositions in a manner which is independent of the crystalline structure of the dye or dyes used in preparing the compositions.

In general, the elements produced by the techniques, of this invention can be employed in any of the well-known electrophotographic processes which require photoconductive layers. One such process is the xerographic process. In a process of this type, an electrophotographic element is held in the dark and given a blanket electrostatic charge by placing it under a corona discharge. This uniform charge is retained by the layer because of the substantial dark insulating property of the layer, i.e., the low conductivity of the layer in the dark. The electrostatic charge formed on the surface of the photoconductive layer is then selectively dissipated from the surface of the layer by imagewise exposure to light by means of a conventional exposure operation such as, for example, by a contact-printing technique, or by lens projection of an image, and the like, to thereby form a latent electrostatic image in the photoconductive layer. Exposing the surface in this manner forms a pattern of electrostatic charge by virtue of the fact that light energy striking the photoconductor causes the electrostatic charge in the light struck areas to be conducted away from the surface in proportion to the intensity of the illumination in a particular area.

The charge pattern produced by exposure is then developed or transferred to another surface and developed there, i.e., either the charged or uncharged areas rendered visible, by treatment with a medium comprising electrostatically responsive particles having optical density. The developing electrostatically responsive particles can be in the form of a dust, i.e., powder, a pigment in a resinous carrier, i.e., toner. A preferred method of applying such toner to a latent electrostatic image for solid area development is by the use ofa magnetic brush. Methods of forming and using a magnetic brush toner applicator are described in the following U.S. Pat. Nos. 2,786,439; 2,786,440; 2,786,441; 2,811,465; 2,874,063; 2,984,163; 3,040,704; 3,1 17,884; and Reissue 25,779. Liquid development of the latent electrostatic image may also be used. ln liquid development, the developing particles are carried to the image-bearing surface in an electrically insulating liquid carrier. Methods of development of this type are widely known and have been described in the patent literature, for example, U.S. Pat. No. 2,907,674 and in Australian Pat. No. 212,315. In dry developing processes, the most widely used method of obtaining a permanent record is achieved by selecting a developing particle which has as one of its components a low-melting resin. Heating the powder image then causes the resin to melt or fuse into or on the element. The powder is, therefore, caused to adhere permanently to the surface of the photoconductive layer. In other cases, a transfer of the electrostatic charge image formed on the photoconductive layer can be made to a second support such as paper which would then become the final print after development and fusing. Techniques ofthe type indicated are well known in the art and have been described in a number of U.S. and foreign patents, such as U.S. Pat. Nos. 2,297,691 and 2,551,582 and in RCA Review" Vol. 15 (1954) pages 469-484.

The following examples are included for a further understanding of the invention.

EXAMPLE 1 A control coating is prepared from. parts by weight of dichloromethane, and nine parts by weight of Bisphenol A polycarbonate resin (Lexan 105, General Electric Co.) which are stirred rapidly in a mechanical mixer for 2 horus at about 20 C. until the resin is completely dissolved, and then six parts by weight of the photoconductor, 4,4'-diethylamino-2,2 "dimethyl-triphenylmethane, are added with further stirring at about 20 C. for 30 minutes. Next, 0.3 parts by weight of 4- (4-dimethyl-aminophenyl)-2,6-diphenylthiapyrylium fluoroborate is added and the solution is stirred for 2 hours after which the composition is filtered through a 2 to 5;]. rated fiber filter cartridge (Fulflo cartridge, Commercial Filter Corp.). The filtered solution is then coated on a poly(ethylene terephthalate) film base carrying a vapor deposited thin conducting layer of nickel. The thickness of the dry control coating is from about 10 to 12 microns. The resultant electrophotographic element is then measured for optical density at 600 land at 690 mu. Next, the element is electrostatically charged under a corona source until the surface potential, as measured by an electrometer probe, reaches about 600 volts. The charged element is then exposed to a 3,000 K. tungsten light source through a stepped density gray scale and also through a short wavelength pass interference filter having 30 percent transmittance at 600 mg. The exposure causes reduction of the surface potential of the element under each step of the gray scale from its initial potential, V,,, to some lower potential, V, whose exact value depends upon the actual amount of exposure in meter-candle-seconds received by the area. The results of these measurements are then plotted on a graph of surface potential V vs. log exposure for each step. The actual positive or negative speed of the photoconductive composition can then be expressed in terms of the reciprocal of the exposure required to reduce the surface potential to any fixed, selected value. Herein, unless otherwise stated, the actual positive or negative speed is the numerical expression of 10 divided by the exposure in meter-candle-seconds required to reduce the 600 v. charged surface potential to a value of 50 v. Speeds thus determined are referred to as positive or negative 50 v. toe speeds. The optical density and electrophotographic speed of this element are shown in table below.

EXAMPLE 2 A composition as in example 1 is prepared and percent of the resultant solution is placed into a high speed shearing blender and sheared for about minutes. The sheared portion of the solution is then added to the remaining 90 percent of the solution which was not sheared. A coating is prepared from this solution after filtering as in example 1. Optical density and electric speed measurements are then conducted as in example I with the results being shown in table 5 below. It is evident that the shearing increases both speed and optical density.

EXAMPLE 3 The materials of example 1 are again used to prepare a coating dope. The procedure of example 1 is modified in that the sensitizing dye is added to the solvent first and stirred for about 2 hours. The resin is then added to the solution with stirring for an additional 2 hours. The photoconductor is next added and the completed solution is stirred rapidly for about 1% hour. The solution is not subjected to shearing. The resultant coating dope is coated as in example I to form an electrophotographic element which is measured for optical density and speed as described above. Both the optical density and electrical speed are improved over the corresponding values obtained when the components are added in the normal order. The resultant element can then be charged, exposed and developed to form visible images using liquid developers ofthe type described in U.S. Pat. No. 2,907,674.

EXAMPLE 4 The procedure of example 3 is followed with the exception that the binder is added first and stirred for 2 hours whereupon the sensitizing dye is added and stirred for 2 hours. Next, the photoconductor is added and the solution is further stirred for minutes. The combined solution is coated as in example 1 and measured for electrical speed and optical density. This procedure is repeated several times with speed measurements being made on each coating. The results are highly erratic with some speeds being considerably lower than others. The results show that merely having the dye and binder in solution before the photoconductor is dissolved do not consistently produce the higher electrical speeds and optical density obtainable by the dye first method of this invention.

EXAMPLE 5 The procedure of example 1 is repeated using twice as much sensitizing dye in the coating composition. The combined solution is coated and measured as in the previous examples. Table 5 shows the results of these measurements. The fact that the optical density and electrical speed are little changed from that of example 1 indicates that only a very slightly greater amount of dye is dissolved in this solution than is dissolved in example 1.

EXAMPLE 6 The procedure of example 2 is repeated, using a 10 percent portion of the solution prepared as in example 5. After the 10 percent portion is sheared, it is added to the remainder of the unsheared solution and coated as in example 1. The resultant element is then measured for optical density and electrical speed. Table 5 shows that the optical density and electrical speeds are slightly greater than those of the sheared composi: tion of example 2 which have the lower dye concentration. However, the sheared composition shows optical density and electrical speed which are only as great as those obtained by the dye first method of example 3 wherein the composition contained a lower dye concentration.

EXAMPLE 7 The dye first procedure of example 3 is repeated again using twice the concentration of dye. On coating the final solution, the resultant electrophotographic element is measured for optical density and electrical speed. The optical density results shown in table 5 indicate that a considerably greater amount of dye is utilized to form the present aggregate composition which results in a nearly twofold increase in electrophotographic speed.

EXAMPLE 8 r The procedure of example 3 is repeated with the exception that 4-(4dimethylaminophenyl)-2,6-diphenylthiapyrylium perchlorate is used as the sensitizing dye. Aggregate formation is spontaneous and complete upon addition of the binder and upon testing the electrophotographic element prepared from this composition, an equivalent result to that obtained in example 3 is obtained.

EXAMPLE 9 The procedure of example 4 is repeated, using twice the concentration of the sensitizing dye. An electrophotographic element formed using this composition is then measured for speed and optical density. Again, erratic results are obtained making it difficult to positively ascertain if even slight in- The procedure of example 3 is repeated using 4- diethylaminotetraphenylmethane as the photoconductor and 4-(4-dimethylaminophenyl)-2,6-diphenylthiapyrylium perchlorate as the sensitizing dye. The composition of the total solids added to the solution is 2 percent by weight of dye, about 37 percent by weight of photoconductor with the remainder comprised of the binder of example 1. After first dissolving the dye, followed by dissolution of the binder and photoconductor, the resultant solution is coated as in example 1 with a coating block temperature of about 15 C. to form an electrophotographic element. This element is then tested for electrical speed and found to have a 100 volt negative toe speed of about 1,100. The element is then tested for 100-cycle regeneration properties. This test comprises subjecting the element to corona discharge and exposure as in example 1 followed by a flooding or erase exposure, all within a period of 3 seconds. This cycle is repeated for 100 times and the charge measured on the photoconductive surface is compared after the first cycle and after the 100th cycle. it is found that after 100 cycles, the maximum charge on the photoconductive surface has not dropped from that of the first cycle. Next, the resultant electrophotographic element is charged, exposed, and developed as in example 3 to form a visible image.

EXAMPLE l l The procedure of example 10 is repeated using 4,4',4"- tris(diethylamino)tetraphenylstannane in one photoconductive composition and diphenyl-bis-(p-diethylaminophenyl)stannane as the photoconductor in a second composition. The first composition has a total solids content of 2 percent by weight of dye, about 60 percent photoconductor and the remainder is binder, and the second composition contains 2 percent dye, about 53 percent photoconductor with the remainder comprised as binder of example 1. The two compositions are each coated on a separate support as in example 1 at a coating block temperature of about 180 C. The resultant elements 1 and 2, respectively, are then tested as in example 10 for electrical speed. Element No. l was found to have a negative l-volt toe speed of about 3,500 and Element No. 2 is found to have a negative lOO-volt toe speed of about 1,700. The two elements are then charged, exposed, and developed as in example I to form good visible images.

EXAMPLE 12 The procedure of example is again repeated using a solids content of 2 weight percent of the dye of example l0, about 62 percent by weight of the photoconductor tetra-pdiethylaminophenylgermane with the remainder comprised of the binder of example 1. The resultant coating dope is then coated on a support as in example 1 at a coating block tem' perature of about C. The resultant electrophotographic element is then tested for electrical speed as in example 1 and found to have a negative 100-volt toe speed of approximately 480. This element is capable of forming good visible images when charged, exposed and developed as in example 1.

EXAMPLE 13 The procedure of example 10 is repeated again with the total solids added to the coating solvent being comprised of 2 percent by weight of the dye of example 10, about 40 percent by weight of the photoconductor of example 1 with the remainder being the binder of example 1. The resultant solution is coated as in the previous examples at a coating block temperature of about [5 C. The electrophotographic element thus formed is tested as in example 10 and found to have a negative l00-volt toe speed of L800. This electrophotographic element can be charged, exposed and developed as in preceding examples to form a visible image.

EXAMPLE 14 The dye first procedure of example 3 is repeated by dissolving 0.375 g. of the dye of that example in 42.5 g. of methylene chloride with stirring for about 2 hours. After dissolution of the dye, 4.5 g. of poly(4,4-isopropylidenedi-phenylcarbonate-block-oxytetramethylene) are added with stirring for about 2 hours to dissolve the polymer. Next, 3 g. of the photoconductor of example 1 are added and the materials are stirred for an additional A hour. The combined dope is then coated onto a conducting support as in example 1 and allowed to dry. The resultant electrophotographic element is then charged in the dark to a surface potential of 600 volts and exposed as in example i. The positive or negative speeds are the numerical expression of l04 divided by the exposure in metercandle-seconds required to reduce the 600 v. charged surface to a potential of500 v. v. shoulder speed) and to a value of 100 v. (100 v. toe speed). The positive shoulder and toe speeds are 3,200 and 320, respectively and the negative shoulder and toe speeds are 2,800 and 500, respectively. After an erasing exposure, this element can be charged, imagewise exposed and developed as in example 3 to form a visible image.

The invention has been described in detail with particular reference to certain preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention.

We claim:

1. A process for forming a photoconductive composition comprising the steps of first substantially completely dissolving at least one pyrylium dye in a halogenated hydrocarbon coating solvent, subsequently adding thereto an electrically insulating polymeric material having an alkylidene diarylene moiety in the recurring unit, thoroughly mixing he dye solu tion containing polymeric material, coating a thin film about 10 microns to about 1,250 microns thick of the resulting composition on a substrate, allowing the film to dry to form a multiphase heterogeneous photoconductive composition having a continuous phase comprising said polymeric material and having a discontinuous phase containing a combination of said dye and polymeric material, said discontinuous phase being visible under 2500X magnification and the radiation absorption maximum for said multiphase composition being substantially shifted from the radiation absorption maximum of said dye and polymer when combined together in a homogeneous state.

2. A process as described in claim 1 wherein said pyrylium dye is selected from the group consisting of pyrylium, selenapyrylium and thiapyrylium dye salts.

3. A process for forming a photoconductive composition comprising the steps of first dissolving in a halogenated hydrocarbon coating solvent at least one sensitizing dye selected from the group consisting of pyrylium and thiapyrylium dye salts, agitating the resultant solution, subsequently adding thereto a photoconductor and a film-forming, electrically insulating polymeric material having an alkylidene diarylene moiety in a recurring unit, thoroughly mixing the dye solution containing said polymeric material and photoconductor, coating a film about 10 microns to about 1,240 microns thick of the resulting composition on a substrate and allowing said film to dry to form a sensitized multiphase heterogeneous photoconductive composition having a continuous phase comprising said polymeric material and having a discontinuous phase containing a combination of said dye and polymeric material, said discontinuous phase being visible under 2500X magnification and the radiation absorption maximum for said heterogeneous composition being substantially shifted from the radiation absorption maximum of said dye and polymeric material in a homogeneous combination.

4. A process for forming an electrophotographic element comprising the steps of first dissolving in a halogenated hydrocarbon coating solvent at least one dye salt having the formula:

wherein:

R and R are aryl radicals selected from the group consisting of phenyl and substituted phenyl radicals having at least one substituent selected from the group consisting of an alkyl radical of from one to six carbon atoms and an alkoxy radical of from one to six carbon atoms;

R is an alkylamino-substituted phenyl radical having from one to six carbon atoms in the alkyl moiety;

X is selected from the group consisting of sulfur and oxygen;

and

Z is an anion;

agitating the resultant solution, subsequently adding an organic photoconductor and an electrically insulating polymeric material having an alkylidene diarylene moiety in the recurring unit, thoroughly mixing the dye solution containing said photoconductor and polymeric material, coating a film about microns to about 1,250 microns thick of the resultant composition on an electrically conductive support, and allowing said film to dry to form a sensitized heterogeneous photoconductive composition having a continuous phase comprising said polymeric material and having a discontinuous phase containing a combination of said dye and polymeric material, said element being characterized by a radiation absorption in a wavelength range different than a wavelength range of radiation absorption for an element carrying identical substituents having a substantially homogeneous combination of said dye and polymeric material.

5. A process as described in claim 4 wherein said polymeric material contains the following moiety in a recurring unit:

wherein:

each R is a phenylene radical; R and R when taken separately. each represent a member selected from the group consisting ofa hydrogen atom, an alkyl radical and an aryl radical; and when taken together, R and R represent the carbon atoms necessary to form a cyclic hydrocarbon radical, the total number of carbon atoms in R and R being up to 19. 6. A process as in claim 1 wherein the coating solvent is selected from the group consisting of a halogenated lower alkane having from one to three atoms.

7. A process as in claim 6 wherein the sensitizing dye is a 2,4,6-triphenylthiapyrylium dye salt.

8. A process as in claim 1 wherein a photoconductor is added to the solution containing said dye and polymer prior to coating a film of the resulting composition.

9. A process as in claim 3 wherein the solvent is dichloromethane.

10. A process as in claim 3 wherein the photoconductor used is an organic photoconductor selected from the group consisting ofa polyarylalkane having the formula:

wherein each of D, E, and G is an aryl radical, J is selected from the group consisting ofa hydrogen atom. an alkyl radical and an aryl radical, at least one of D, E, nd G containing an amino substituent; a Group Illa organometallic compound fluoroborate and 4-( 4-dimetliylaminophenyl )-2 ,6-diphenylthiapyrylium perchlorate.

13. A process as in claim 3 wherein the amount of sensitizing dye added is from about be to about 30 percent by weight of the total solids added to the coating solvent and wherein the amount of photoconductor added is from about 10 to about percent by weight of the total solids added to the coating solvent.

14. A process as in claim 3 wherein the polymer is a polycarbonate. 

2. A process as described in claim 1 wherein said pyrylium dye is selected from the group consisting of pyrylium, selenapyrylium and thiapyrylium dye salts.
 3. A process for forming a photoconductive composition comprising the steps of first dissolving in a halogenated hydrocarbon coating solvent at least one sensitizing dye selected from the group consisting of pyrylium and thiapyrylium dye salts, agitating the resultant solution, subsequently adding thereto a photoconductor and a film-forming, electrically insulating polymeric material having an alkylidene diarylene moiety in a recurring unit, thoroughly mixing the dye solution containing said polymeric material and photoconductor, coating a film about 10 microns to about 1,240 microns thick of the resulting composition on a substrate and allowing said film to dry to form a sensitized multiphase heterogeneous photoconductive composition having a continuous phase comprising said polymeric material and having a discontinuous phase containing a combination of said dye and polymeric material, said discontinuous phase being visible under 2500X magnification and the radiation absorption maximum for said heterogeneous composition being substantially shifted from the radiation absorption maximum of said dye and polymeric material in a homogeneous combination.
 4. A process for forming an electrophotographic element comprising the steps of first dissolving in a halogenated hydrocarbon coating solvent at least one dye salt having the formula:
 5. A process as described in claim 4 wherein said polymeric material contains the following moiety in a recurring unit: wherein: each R is a phenylene radical; R4 and R5, when taken separately, each represent a member selected from the group consisting of a hydrogen atom, an alkyl radical, and an aryl radical; and when taken together, R4 and R5 represent the carbon atoms necessary to form a cyclic Hydrocarbon radical, the total number of carbon atoms in R4 and R5 being up to
 19. 6. A process as in claim 1 wherein the coating solvent is selected from the group consisting of a halogenated lower alkane having from one to three atoms.
 7. A process as in claim 6 wherein the sensitizing dye is a 2,4, 6-triphenylthiapyrylium dye salt.
 8. A process as in claim 1 wherein a photoconductor is added to the solution containing said dye and polymer prior to coating a film of the resulting composition.
 9. A process as in claim 3 wherein the solvent is dichloromethane.
 10. A process as in claim 3 wherein the photoconductor used is an organic photoconductor selected from the group consisting of a polyarylalkane having the formula: wherein each of D, E, and G is an aryl radical, J is selected from the group consisting of a hydrogen atom, an alkyl radical and an aryl radical, at least one of D, E, nd G containing an amino substituent; a Group IIIa organometallic compound having at least one aminoaryl radical attached to a Group IIIa metal; a Group IVa organometallic compound having at least one aminoaryl radical attached to a Group IVa metal; a Group VA organometallic compound having at least one aminoaryl radical attached to a Group VA metal; and a polyarylamine.
 11. A process as in claim 3 wherein the photoconductor is selected from the group consisting of 4,4''-diethylamino-2,2''-dimethyltriphenylmethane, 4-diethylaminotetraphenylmethane; 4,4'', 4''''-tris(diethylamino)tetraphenylstannane, diphenyl-bis(p-diethylaminophenyl)stannane and tetra-p-diethylaminophenylgermane.
 12. A process as in claim 3 wherein the sensitizing dye is selected from the group consisting of 4-(4-dimethylaminophenyl)-2,6-diphenylthiapyrylium fluoroborate and 4-(4-dimethylaminophenyl)-2,6-diphenylthiapyrylium perchlorate.
 13. A process as in claim 3 wherein the amount of sensitizing dye added is from about 1/2 to about 30 percent by weight of the total solids added to the coating solvent and wherein the amount of photoconductor added is from about 10 to about 80 percent by weight of the total solids added to the coating solvent.
 14. A process as in claim 3 wherein the polymer is a polycarbonate. 